1. Field of the Invention
The present invention relates to a light emitting diode (hereinafter, referred to as an "LED") display device including a plurality of light emitting blocks or dots arranged in a matrix, each light emitting block having LEDs for three or more colors, and a method for controlling such an LED display device.
2. Description of the Related Art
In color video display devices, color display is obtained by color mixing of red primary color, green primary color and blue primary color. Conventionally, a color TV signal is mainly used for a video signal for color video display. In an LED display device including a red LED, a green LED and a blue LED, only a red LED is turned on in accordance with a red color signal, only a green RED is turned on in accordance with a green color signal, and only a blue RED is turned on in accordance with a blue color signal.
Table 1 shows chromaticity values of red, green and blue colors obtained by exemplary standards for color TV broadcasting.
TABLE 1 ______________________________________ NTSC standards HDTV studio standards (SMPTE 170M) (CCIR Rec709) Primary color x y x y ______________________________________ Red 0.630 0.340 0.640 0.330 Green 0.310 0.595 0.300 0.600 Blue 0.155 0.070 0.150 0.060 ______________________________________
As shown in Table 1, the x values of the red color for the NTSC standards (SMPTE 170M) and the HDTV standards are substantially equal to each other, and the y values of the red color for the NTSC standards and the HDTV standards are substantially equal to each other. The x values and the y values of each of the green and blue colors for the NTSC standards (SMPTE 170M) and the HDTV standards are also equal to each other. CRTs (cathode ray tubes) used in current color TVs have substantially equal values to those shown in Table 1. Thus, the video reproducibility obtained by the CRTs is satisfactorily high.
Table 2 shows chromaticity values of red, green and blue colors obtained by LEDs which are currently in practical use.
TABLE 2 ______________________________________ Chromaticity Color x y ______________________________________ Red 0.72 0.28 Green 0.17 0.70 Blue 0.13 0.075 ______________________________________
The chromaticity values of the blue color in Tables 1 and 2 are proximate to each other, but the chromaticity values of each of the red and green colors in Tables 1 and 2 are different from each other.
This is confirmed from the chromaticity diagram in FIG. 5, in which the chromaticity values of the blue color for HDTV and LED are substantially equal to each other, but the chromaticity values of each of the red and green colors for HDTV and LED are different from each other.
As can be appreciated from this, the conventional method for operating an LED display device including the steps of turning on only the red LED in accordance with the red color signal, turning on only the green LED in accordance with the green color signal, and turning on only the blue LED in accordance with the blue color signal causes inferior color reproducibility for red and green, thus resulting in unnatural color display.
Japanese Laid-Open Publication No. 8-272316, for example, proposes simultaneously turning on two green LEDs for emitting light components having different wavelengths in order to compensate for the inferiority of the green color. Such a system disadvantageously requires four LEDs and four LED driving circuits.